Radio Occultation Measurements of the Radio Wave Absorption and the Sulfuric Acid Vapor Content in the Atmosphere of Venus

The results of the determination of centimeter ( = 5 cm) radio waves absorption in the radio occultation experiments, carried out using the Venera-15and Venera-16spacecraft, are presented. The altitude distribution of the absorber substance is analyzed. The absorbing layer is shown to exist at altitudes of 64 to 58 km in the near-polar regions of the planet. At middle latitudes such an absorbing layer was not found. In the altitude range from 56 to 46 km the radio wave absorption by the sulfuric acid (H₂SO₄) vapor is observed. The content of the sulfuric acid vapor is shown to increase with decreasing altitude: in the mid-latitude region at altitudes of 56.7 and 53 km it equals 5 and 20 ppm, respectively, and at polar latitudes the same content of H₂SO₄vapor is observed at altitudes of 51.2 and 47 km, respectively. A comparison of these results with the data of radio wave absorption in the = 13 cm band, obtained in the Pioneer Venus Orbiterradio occultation experiments, leads to the conclusion that the obtained values of the sulfuric acid vapor content well agree in the regions of overlap of the data.     

Kink mode m = 1 in magnetic tube with discontinuous magnetic field

In this paper, we study conditions of realization and stability of kink modes with azimuthal wave numbers $m=\pm 1$ in cylindrical plasma flex with twisted magnetic field and homogeneous current along its axis. We assume permanent axial magnetic field both inside and outside the flex, surrounded by currentless plasma. Azimuthal magnetic field decreases inversely proportional to the distance from the boundary beyond the flex. We derived dispersion equations for stable and unstable modes in approximation of “thin” plasma flex. The analysis of equations has been provided for the case of discontinuous axial magnetic field on flex’s boundary. Conditions of propagation of wave modes have been defined. It was shown, that unstable modes can be implemented in certain interval of longitudinal wavenumbers. Results can be applied for the interpretation of solar magnetic tubes behavior, using measurements, provided by spacecrafts.     

Non-stationarity and cross-correlation effects in the MHD solar activity

The analysis of turbulent processes in sunspots and pores which are self-organizing long-lived magnetic structures is a complicated and not yet solved problem. The present work focuses on studying such magneto-hydrodynamic (MHD) formations on the basis of flicker-noise spectroscopy using a new method of multi-parametric analysis. The non-stationarity and cross-correlation effects taking place in solar activity dynamics are considered. The calculated maximum values of non-stationarity factor may become precursors of significant restructuring in solar magnetic activity. The introduced cross-correlation functions enable us to judge synchronization effects between the signals of various solar activity indicators registered simultaneously.     

Changes in hyperspectral reflectance signatures of lettuce leaves in response to macronutrient deficiencies

The adaptation of specific remote sensing and hyperspectral analysis techniques for the determination of incipient nutrient stress in plants could allow early detection and precision supplementation for remediation, important considerations for minimizing mass of advanced life support systems on space station and long term missions. This experiment was conducted to determine if hyperspectral reflectance could be used to detect nutrient stress in Lactuca sativa L. cv. Black Seeded Simpson. Lettuce seedlings were grown for 90 days in a greenhouse or growth chamber in vermiculite containing modified Hoagland’s nutrient solution with key macronutrient elements removed in order to induce a range of nutrient stresses, including nitrogen, phosphorus, potassium, calcium, and magnesium. Leaf tissue nutrient concentrations were compared with corresponding spectral reflectances taken at the end of 90 days. Spectral reflectances varied with growing location, position on the leaf, and nutrient deficiency treatment. Spectral responses of lettuce leaves under macronutrient deficiency conditions showed an increase in reflectance in the red, near red, and infrared wavelength ranges. The data obtained suggest that spectral reflectance shows the potential as a diagnostic tool in predicting nutrient deficiencies in general. Overlapping of spectral signatures makes the use of wavelengths of narrow bandwidths or individual bands for the discrimination of specific nutrient stresses difficult without further data processing.     

The Solar Sail Materials (SSM) project – Status of activities

SSM (Solar Sail Materials) is an on-going project for the European Space Agency (ESA) relying on past and recent European solar sail design projects. It aims at developing and testing future technologies suitable for large, operational solar sailcrafts.     

Seasonal variation of surface refractivity over Nigeria

The seasonal variation of surface refractivity over Nigeria was studied using two years in-situ meteorological data from eight locations over Nigeria. The result shows that the surface refractivity generally has higher value during rainy season than dry season at all location studied. The results also show that the value of surface refractivity increases from arid region in the north to the coastal area in south. The results also show that local meteorology plays a very important role in refractivity variation.     

Measuring the matter distribution within z = 0.2 cluster lenses with XMM-Newton

We present an analysis of seven clusters observed by XMM-Newton as part of our survey of 17 most X-ray luminous clusters of galaxies at z  0.2 selected for a comprehensive and unbiased study of the mass distribution in massive clusters. Using the public software FTOOLS and XMMSAS we have set up an automated pipeline to reduce the EPIC MOS and pn spectro-imaging data, optimized for extended sources analysis. We also developped a code to perform intensive spectral and imaging analysis particularly focussing on proper background estimate and removal. XMM-Newton deep spectro-imaging of these clusters allowed us to fit a standard β-model to their gas emission profiles as well as a standard MEKAL emission model to their extracted spectra, and test their inferred characteristics against already calibrated relations.     

Probing the first stars and black holes in the early Universe with the Dark Ages Radio Explorer (DARE)

A concept for a new space-based cosmology mission called the Dark Ages Radio Explorer (DARE) is presented in this paper. DARE’s science objectives include: (1) When did the first stars form? (2) When did the first accreting black holes form? (3) When did Reionization begin? (4) What surprises does the end of the Dark Ages hold (e.g., Dark Matter decay)? DARE will use the highly-redshifted hyperfine 21-cm transition from neutral hydrogen to track the formation of the first luminous objects by their impact on the intergalactic medium during the end of the Dark Ages and during Cosmic Dawn (redshifts z = 11–35). It will measure the sky-averaged spin temperature of neutral hydrogen at the unexplored epoch 80–420 million years after the Big Bang, providing the first evidence of the earliest stars and galaxies to illuminate the cosmos and testing our models of galaxy formation. DARE’s approach is to measure the expected spectral features in the sky-averaged, redshifted 21-cm signal over a radio bandpass of 40–120 MHz. DARE orbits the Moon for a mission lifetime of 3 years and takes data above the lunar farside, the only location in the inner solar system proven to be free of human-generated radio frequency interference and any significant ionosphere. The science instrument is composed of a low frequency radiometer, including electrically-short, tapered, bi-conical dipole antennas, a receiver, and a digital spectrometer. The smooth frequency response of the antennas and the differential spectral calibration approach using a Markov Chain Monte Carlo technique will be applied to detect the weak cosmic 21-cm signal in the presence of the intense solar system and Galactic foreground emissions.     

Solar activity dependence of total electron content derived from GPS observations over Mbarara

Vertical total electron content (VTEC) observed at Mbarara (geographic co-ordinates: 0.60°S, 30.74°E; geomagnetic coordinates: 10.22°S, 102.36°E), Uganda, for the period 2001–2009 have been used to study the diurnal, seasonal and solar activity variations. The daily values of the 10.7 cm radio flux (F_10.7) and sunspot number (R) were used to represent Solar Extreme Ultraviolet Variability (EUV). VTEC is generally higher during high solar activity period for all the seasons and increases from 0600 h LT and reaches its maximum value within 1400 h–1500 h LT. All analysed linear and quadratic fits demonstrate positive VTEC-F_10.7 and positive VTEC-R correlation, with all fits at 0000 h and 1400 h LT being significant with a confidence level of 95% when both linear and quadratic models are used. All the fits at 0600 h LT are insignificant with a confidence level of 95%. Generally, over Mbarara, quadratic fit shows that VTEC saturates during all seasons for F_10.7 more than 200 units and R more than 150 units. The result of this study can be used to improve the International Reference Ionosphere (IRI) prediction of TEC around the equatorial region of the African sector.     

GNSS single frequency ionospheric range delay corrections: NeQuick data ingestion technique

A study of the performance of the NeQuick model and the Klobuchar model for GNSS single frequency range delay correction on a global scale was done using data for moderate solar activity. In this study NeQuick was used in the way intended for Galileo. This study is to assess the performance of the two models at each ionospheric geographic region during moderate solar activity as previously published studies were concentrated only on high solar activity. The results obtained showed that NeQuick outperformed Klobuchar for the whole year at the three geographical regions of the ionosphere. In terms of monthly root mean square of mismodeling, NeQuick outperformed Klobuchar by 15 TECU or more at low-latitudes, 5 TEC or more at mid-latitudes, and 1 TECU or more at high-latitudes.